(1) Field of the Invention
The field of art to which this invention pertains is package-making and, more particularly, it is directed to vacuum skin-packaging.
More specifically, this invention relates to a method of and apparatus for packaging a product, such as a piece of meat, in thermoplastic film. In such method, an upper thermoplastic film is moved downwardly by means of a vacuum chamber over the product and into contact with a lower thermoplastic film on a conveyor belt. The belt which has openings along its edges, moves over a fixed vacuum plate having apertures at its edges and the space around the product is evacuated through these openings and apertures prior to pushing the upper film into skin-like engagement with the product and into heat-sealing contact with the lower film thereby to form a vacuum skin-package.
(2) Description of the Prior Art
Packaging methods and apparatus of this general type are old. It is known, for example, to package an article by pushing an upper film into engagement with the article and a lower film by exerting air pressure on the upper film, after evacuating the space around the product, and various packaging techniques have been utilized to do this.
U.S. Pat. No. 2,690,593 to Abercrombie, which is exemplary of the prior art, for example, discloses moving a heater housing and platen towards a base to envelop an article positioned thereon in a plastic sheet, followed by subjecting the surface of the plastic sheet to reduced pressure to shrink it about the article.
U.S. Pat. No. 2,799,589 to Grinstead et al., another example of this type art, discloses placing a product within packaging material, the edges of which are clamped to produce a fluid tight joint, after which a greater pressure is applied to the outer surface of the material than that existing on the inner surface of the material to make a vacuum skin-package.
Further, U.S. Pat. No. 1,856,694 to Correvont shows a device for laminating a sheet of pyroxylin onto a shaped article, which device has means for gripping and heating the sheet and for forcing the shaped article against the sheet to produce a partial wrapping of the sheet around the shaped article, and means for producing lesser pressure on the article side of the sheet and greater pressure on the opposite side thereof to complete the wrapping of the heat-plasticized sheet around the upper surfaces of the article.
Australian Pat. No. 245,774 describes a noncontinuous vacuum skin-packaging process wherein an article to be packaged is placed on a lower packaging member and inserted within a lower portion of a two-part vacuum chamber. An upper web piece is positioned across the lower part of the vacuum chamber and then the upper part of the chamber is brought into engagement with the lower portion to clamp the piece of upper web between the upper and lower vacuum chambers, and finally the upper web is forced down and around the article and the surrounding portion of the lower packaging member to form a vacuum skin-package.
In further teachings of related packaging techniques in this area, U.S. Pat. No. 3,491,504 to Young et al. shows a packaging method in which a heated upper film is draped over the product while preventing premature sealing of it to a lower packaging member while air is removed between the film and the packaging member, after which the film is pushed against the product and the packaging member to form a heat-sealed, skin-packaged product.
And, lastly, U.S. Pat. No. 3,910,008 to Johnson shows a vacuum packaging system whereby upper and lower films are vacuum sealed about an article at a sealing station, after the space around such article is evacuated.
In the Johnson patent, the article being packaged is placed on a lower embossed film having upwardly extending projections and vacuum is drawn about the edges of this lower film and an upper film positioned above the article and pulled tightly thereabout by such vacuum. The projections allow substantially complete evacuation of air from the enclosed article before the films become completely sealed together thereby to form an airtight package, using this system.
In an important aspect of such system, the lower film with the article thereon, is conveyed to the sealing station by means engagable with the lower film at a point downstream from the sealing station. Such conveying system includes first and second support sections, a drive roll and a pair of friction wheels. The wheels frictionally engage the flattened side portions of the completed package in the nip between the wheels and the drive roller. Since the lower film is continuous, fresh film is drawn from a storage roll or from an embossing assembly through the apparatus in an amount about the distance each successive package is moved. The amount of rotation is predetermined so that the appropriate amount of film will be drawn into the sealing section.
The lower embossed film with its projections directed upwardly is pulled through the first and second support sections to the sealing section. At this location the housing descends over the product and the upper film, which is in a softened state and is secured to the periphery of this housing by vacuum, stretches over the product while the housing continues its downward movement. Simultaneously air is evacuated from the edges of the embossed lower film. As the upper film continues to be lowered, air is removed from the area about the product and such air evacuation continues even after the upper film has made initial contact with the top surfaces of the projections of the lower film. After substantially all the air is removed, the somewhat resilient projections become collapsed due to the pressure differential between the atmosphere and the reduced pressure between the films. At this point the upper film commences to bond to the lower film at the annular area of their overlap about the product periphery and this continues until sealing is completed and the vacuum package is formed.
A problem with the above teachings, and with the other known art, is their failure to give to the vacuum skin-packaging art, a relatively simple means and method of making a package, such as is found in the method and apparatus of this invention, in which apertures in a conveyor belt moving over a fixed plate are aligned with openings in the plate to permit evacuation of the space around a product being packaged, after a movable one-part vacuum chamber moves an upper film over the product and into contact with a flat lower film, which films are then pushed and sealed together to form a vacuum skin-package.